This randomized, double-blind Phase IV trial will determine whether the gradual initiation of trimethoprim/Sulfamethoxazole (TMP/SMX) suspension for primary pneumocystis carinii pneumonia (PCP) prophylaxis reduces the incidence of adverse events (those that are treatment-limiting and those that are not treatment-limiting), as compared with the routine daily initiation of TMP/SMX DS tablets in HIV-infected subjects. (ACTG 268)